Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SHORT GLASS FIBERS COVERED WITH POLYMERIC MATERIALS
BACKGROUND OF THE INVENTION
DT-AS (German Published Specification) l,244,347
(respectively British Patent 1 047 840) describes a process
for the manufacture of short glass fibers which can be
metered. According to this, short glass fibers, which are
very difficult to meter by the customary processes, are
converted into the form of granules by treatment in, for
example, organic solvents. The said patent specification
also contains a note that the solvents can contain, for
example, sizes.
SUMMARY OF THE INVENTION
The present invention relates to spheres of high
molecular weight thermoplastics filled with fibers selected
from the group consisting of mineral fibers, carbon fibers
and other inorganic fibers having an average diameter of
between l and 15mm and to a process for the manufacture of
these spheres comprising
a. mixing said fibers having an average length
of between 0.1 and 10 mm in a l to 30~ strength
by weight solution of high molecular weight
thermoplastics having a viscosity of less
than 1000 cP;
, .
b. rotating the mixture of said fibers and high
molecular weight thermoplastics solution in
an apparatus which rotates about an axis
which passes through said apparatus to form
` spheres of high molecular weight thermoplastics
filled with said fibers; and
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c. subsequently drying the spheres of high
molecular weight thermoplastics filled
with said fibers to free said spheres
from solvent.
BRIEF DESCRIPTI~N OF THE DRAWING
The drawing is a schematic of a ~ylindrical vessel
` which can be rotated about its longitudinal axis fitted with
four metal sheets arranged radially along the vessel wall in
which the spheres of high molecular weight thermoplastics
filled with short glass fibers according to the present
invention may be prepared.
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i DETAILED DESCRIPTION OF THE INVENTION
The short glass fibers according to the invention,
which are covered with polymeric materials, have an extremely
stable sperical form even if they only contain 1-30% by
weight, preferably 1-5% by weight, of high-polymer plastics,
and can then only be deformed by high pressure. Even in
a prolonged shaking test they show practically no abrasion.
They can be metered in a simple manner, for example, by
. 20 means of belt weighers or by apparatuses working on a
volumetric principle. The advantage of the short glass fiber
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coated with plastic, over the state of the art is the high
resistance to pressure, which is of use, for example, ln the
case of silo storage, and the abrasion resistance. The
high abrasion resistance is ~elieved to be due to the fact
that the glass fibers are virtually entirely encased in
a spherical shell. This surprising result is evidently
due to the fact the major portion of the polymeric plastic
is deposited on the surface of the glass fiber. This encap-
sulation also almost totally obviates the hazard of glass
fiber dust which is encountered when using meterable glass
fibers such as those taught by DT-AS (German Published
Specification) 1,244,347 respectively British equivalent Patent
1 047 840.
A further surprising advantage of the shoxt glass
fibers, coated with plastic according to the invention is
` 15 that when incorporating glass fibers into plastics which
according to the present invention are also used as the
coating material, disintegration of the glass fibers by a
grinding action, for example, in the screw machine which are
`~ suitable for the incorporation of the glass fibers, is greatly
reduced. Therefore, the technically involved metering of
the glass fibers into the previously fused plastic mass is
no longer required. In addition, glass fiber-reinforced
plastic molding compositions of higher quality are produced.
When using the short glass fibers, coated with
plastic, according to the invention, it is possible to feed
plastics, together with glass fiber material, into the
screw machines through a hopper of the machine and thus to
produce glass fiber-reinforced plastics in a simple manner.
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When using the short glass ~ibers according to
the invention, material abrasion in the screw machine is
also reduced.
The plastic-coated glass fibers according to the
invention, containing about 5-30% by weight of plastic
coatings, are suitable for use as the base material for the
manufacture of glass fiber mats. In the process of manu-
facture of the glass mats, the plastic spheres, filled with
short glass fibers according to the invention are converted
; 10 to the desired shaped articles in ~ press at molding tempera-
; tures above the melting ranges of the plastics which have
; been applied to the short glass fibers. The mats are dimen-
sionally very stable and have an abrasion-resistant surface~
; They can be stored, and handled, in a simple manner. Special
15 precautionary measures prior to possible further processing
; are no longer necessary.
The short glass fibers coated with plastic accord-
ing to the invention are manufactured in a simple manner
in known apparatuses and the manufacture can be carried
out continuously or discontinuously.
., ~
A suitable process is to mix a plastic solution,
which is obtained by dissolving the plastic in a suitable
solvent, and the short glass fibers in a vessel which rotates
about an axis and to rotate the vessel for a period of
~ 25 2-60 minutes. Thereafter, the drying can be effected in the
< same apparatus or in a separate part of the apparatus, by
evaporating the solvents at elevated temperatures or by
f using vacuum. After the drying has taken place, the plastic-
coated short glass fibers or plastic spheres filled with
30 short glass fibers can be removed from the apparatuses, and
can be employed for the applications mentioned.
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Suitable apparatuses ~or the manufacture of the
plastic-coated short glass fibers are, for example, drums,
rotary tubes and tumbler driers. It is frequently desired
to ensure good ~istribution of the charge by providing
inserts in the apparatus and thereby at the same ~ime avoiding
the glass fiber material slipping down the wall of the vessel.
To achieve optimum results with regard to duration
of treatment and shape and size distribution of the plastic
spheres filled with short glass fibers, it is of advantage
so to choose the ratio of the amount of glass fiber to
the polymer solution such that after conversion of the short
~; glass fibers to the plastic spheres, there is no polymer
solution l~ft present; in other words, the polymer solution
should be absorbed practically quantitatively on the short
glass fiber. This is the case if the weight ratio of the
amount of glass fibers to the polymer solution varies
approximately within the limits 1:0.5 to 1:5. Parameters
which determine the optimum ratio are, for example, the
solids content and the viscosity of the polymer solution on
,
the one hand, and the nature of the short glass fibers
such as average fiber length, diameter and wettability, on
the other.
It has proved desirable to utilize about 1/4 to
2/3 of the available reactor volume when manufacturing the
plastic-coated short glass fibers.
The moist short glass fibers are generally manu-
factured under normal pressure at room temperature~ but
always below the boiling point of the solvents used. Raising
the temperature produces no direct advantage with regard to
accelerated performance of the process, but can be of
importance as regards the subsequent drying process.
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The speed of rotation of the apparatuses is
generally not a critical parameter. However, to avoid
rather long treatment times, it is desirable to work at the
upper limit of the permissible rates of revolution of the
particular apparatus. Circumferential velocities of the
rotating vessel which cause intense turbulent mixing of
th~ cnarge, are to be avoided. Circumferential speeds of
0.1 m/sec to 5 rn/sec, preferably 0.1 m/sec to 1 m/sec, have
proved of value.
The plastic-coated short glass fibers in general
have an average diameter between 1 mm and 15 mm and pre-
ferably between 2 mm and 10 mm. The size of the granules
can ~e reduced by prolonged treatment in the rotating
apparatuses.
; 15 The concentration of the polymer solutions is in
general between 1 and 30~ by weight. It depends primarily
on the amount of plastic with which the short glass fibers are
to be coated. The process can be carried out without problems
if the viscosities of the polymer solutions are <1,000 cP.
~0 The drying process is also carried out according
~ to known techniques and in known apparatuses. In addition
- to the discontinuously operating apparatuses such as
drying cabinets, drying towers, tumbler driers and heated
vessels, continuously operating apparatuses such as rotary
tubes, disc driers and paddle driers are also suitable.
In general, drying takes place very rapidly since
the plastic-coated short glass fibers have a capillary ac~ion
and convey the solvents to the surface. This also explains
the fact that the plastics preferentially cover the surfaces
of the short glass fibers. The temperatures are so chosen,
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in accordance with the solvents used, that the melting points
of the plastics are not reached, the margin of safety being
approximately 50C. It is advisable to carry out the drying
with exclusion of air. Only in the case of high-boiling
point solvents is the use of vacuum or direct heating with
hot inert gases or steam necessary, and in such cases these
methods can be considered.
During the drying process, there is no further
direct need for mixing the charge, but mixing can be of
importance from the point of view of better heat transfer,
and is advisable in such cases.
Suitable short glass fibers are the commercially
available products such as are used, for examplel to manu-
~ facture glass fiber-reinforced thermoplastics, these products
- 15 having fiber lengths between 0.1 and 10 mm, preferably
between 0.1 and 6 mm. These materials an be employed with and
without sizes and with and without adhesion promoters, without
causing any disadvantages. No special measures are required
before these fibers are used.
; 20 The high-molecular thermoplastics which are
soluble in the organic solvents mentioned later are suitable
- for co~ering and coating the short glass fibers with plastics.
; The following should be mentioned, inter alia: vinyl ~;
` polymers such as polystyrene, polystyrene-acrylonitrile,
, 25 polymethyl methacrylate, polyacrylonitrile, ethylene polymers
'fl and propylene polymers and polyvinyl chloride, and polycon-
densates such, as for example, aromatic polycarbonates, poly~
esters, cellulose esters, polyamides, polyphenylene oxide,
polysulphones and polysilicones. The molecular weights
(Mn) of these thermoplastics should preferably be between
10,000 and 300,000.
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It is also possible to use non-thermoplastic
plastics, for example, unsaturated polyester resins, phenolic
resins or polyurethanes, with preferred molecular weights
(Mn) between 3,000 and 20,000. These plastics are pre-
ferentially used for the manufacture of the glass fiber mats.When they are used to manufacture plastic-coated short glass
fibers it is necessary to ensure that the process temperature
used does not produce curing of the polymer. This is not
a danger when using low-boiling solvents such as, for example,
methylene chloride, chloroform, benzene or petroleum ether.
Low temperatures can be ensured and such problems avoided
by drying in vacuo. Virtually the only polymeric materials
which are unsuitable for use as polymeric coating substances
are those which lead to stickiness. However, this is
; 15 essentially the case for extremely low-molecular products.
Solvents which can be used for the plastics
mentioned, in the abovementioned concentrations of 1% by
weight to 30% by weight, are the substances known, and
described in the literature. As already mentioned, low-
20 boiling solvents are used in particular. The followingmay be mentioned as examples: methylene chloride, chloroform,
1,2-dichloroethane, ethyl acetate and butyl acetate, acetone,
benzene and toluene. For polyamides specifically, formic
~ acid can be used. For aromatic polyesters, a mixture of
trifluoroacetic acid and methylene chloride or chloroform
has proved of value.
The plastic-coated short glass fibers or plastic
spheres filled with short glass fibers are used to manu-
facture glass fiber-reinforced thermoplastics and to manu-
facture glass fiber mats.
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In addition to the coating of glass fibers, other
fiber materials, for example mineral fibers or carbon fibers
or other inorganic fibers can also be coated with plastics
by this process.
EXAMPLES
A. Apparatuses
Two apparatuses were used for the manufacture
of the plastic-coated short glass ~ibers.
Apparatus 1 consists of a cylindrical vessel of
400 mm diameter and 800 mm length, with a useful capacity
of approximately 100 liters. This vessel is fitted with
four 50 mm wide metal sheets arranged radially along the
vessel wall. The vessel can be rotated about its longitu-
dinal axis by a device. (see the Figure)
Apparatus 2 consists of a tumbler drier (diameter1000 mm, length 1300 mm, useful capacity 700 liters), which
can be heated, and the axis of rotation of which runs
diagonally. A connection to a vacuum unit provides the
possibility of operating this apparatus under vacuum.
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B. Plastics
The following plastics are employed:
a) Bisphenol A (2,2-bis-(4-hydroxyphenyl)propane)
polycarbonate; nrel 1.289 (0.5% strength in methylene chloride).
b) Polystyrene; nrel 1.59 (0.5% strength in
methylene chloride).
c) Polystyrene-acrylonitrile (80/20); nrel 1.70
(0.5% strength in methylene chloride).
d) Polymethyl methacrylate; nrel 1.345 (0.5%
strength in methylene chloride).
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e) Polyethylene glycol terephthalate; nrel 1.34
~0.5% in 50:50, phenol/1,2-dichloroethane).
f) Polyester based on fumaric acid and propoxylated
bisphenol A (2,2-bis-(4-hydroxyphenyl)propane); number average
molecular weight (~n) approximately 3,000.
~; C. Glass Fibers
Two types of glass fibers are employed.
I. Ground short glass fibers; average fiber length
230~, diameter 13~, proportion of powder (<50~) 5~.
II. Long glass fiber: average fiber length 6.0 mm,
diameter 15~, proportion of powder (<50~) approximately 1%.
i
EXAMPLES 1-23
Glass fibers and plastic solutions are treated,
; and subsequently freed from solvents by drying, in
apparatuses 1 and 2 which have been described, and under the
conditions specified in Table 1.
The average diameter of the plastic-coated short
glass fibers obtained and, in the case of some products,
~he size distribution is determined. These data are
summarized in Table 2.
.
In a further test, the exposure to pressure of the
plastic-coated short glass fibers are determined. In this
test, a plastic-coated short glass fiber sphere of 5 mm
`~ diameter is exposed to a weight of 5 kg and its relative
i
^ 25 deformation in the direction of the force is measured. The
values for a short glass fiber sphere not coated with plastic
: -:
is quoted for comparison.
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EXAMPLE 24
70 parts by weight of polycarbo~ate and 30 parts
by weight of the coated short glass fibers obtained rom
Example 15 are converted to a glass ~iber-reinforced poly-
carbonate 24a in a twin screw extruder (screw diameter 120 mm).The throughput is 500 kg~hour. In a parallel experiment,
commercially available short glass fibers (polycarbonat~ 24b)
and short glass fibers which can be metered, manufactured
according to DT-AS (German Published Specification) 1,244,347
(polycarbonate 24c) are employed.
While a belt weigher suffices for metering the
plastic-coated short glass fibers and allows dust-free opera-
tion, a feed screw must be used for metering the glass
fibers when manufacturing polycarbonate 24b; the maximum
throughput in this case is 300 kg/hr. When manufacturing
polycarbonate 24c, severe dustiness is observed when using
a belt weigher for metering. The metering device is
heavily covered with dust after only one hour of operation.
: The operators have to wear dust-protection clothing.
The mechanical properties of the polycarbonates
produced are tested. The distribution of glass fiber
lengths and the proportion of powder, are determined.
. .
Example Polycarbonates
24a 24b 24c
.. . .Notched impact strength (kp/cm) 8.3 4.7 6.6
Impact strength (kp/cm)58.4 32.9 40.8
Flexural strength (kp/cm )1,5601,280 1,310
' E-modulus (kp/cm2) 62,000 53,000 54,000
- Average glass fiber
length (~) 145 105 110
Proportion of powder
~ ( <50~ ~, % 7 18 15
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TABLE 2
Product Plastic sphere si~e distribution Deformation
from Ex- Average Proportion (%), 5 kg
ample No. Value 2 mm (%) 10 mm (~) load, size of
(mm) or less or more plastic spheres
5 mm
Comparison
x) 4.4 < 5 <10 40 - 60
1 4.7 < 5 < 5 10 - 15
3 5.2 < 5 < 5 <10
4 3.9 < 5 <10 ~ 5
6.8 <10 <10 ~10
6 3.5 < 5 < 5
8 2.9 <10 ~ 5
4.2 < 5 < 5
16 7.5 < 5 <15
21 3.6 < 5 <10
x) without plastic coating according to DT-AS (German
Published Specification) 1,244,347; solvent: methylene
chloride~
Although the invention has been described in detail `.
in the foregoing for the purpose of illustration, it is to be
understood that such detail is solely for that purpose and
that variations can be made therein by those skilled in the
art without departing from the spirit and scope of the
invention except as it msy be limited by the clsims.
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